The South American polka dot tree frog initially appears unremarkable. But researchers in Argentina recently got a huge surprise when they shone an ultraviolet light on it, revealing that the creature is actually fluorescent and glows bright blue-green.

The fluorescence is "unprecedented" in amphibians, the researchers said in a recent paper published in Proceedings of the National Academy of Sciences. It means that "short-wavelength electromagnetic radiation is absorbed and then reemitted at longer wavelength."

The phenomenon had previously been documented primarily in certain fishes and sea turtles, though not in amphibians. And among land-dwelling vertebrates, according to the scientists, it had been spotted in parrots.

The frog also had a second surprise for the scientists, as co-author Norberto Peporine Lopes, a chemist at the University of Sao Paulo, tells The Two-Way. The chemical compounds causing the frog to glow are "amazing and it's a new chemistry," he says.

"Three molecules — hyloin-L1, hyloin-L2 and hyloin-G1 — in the animals' lymph tissue, skin and glandular secretions were responsible for the green fluorescence," according to an article in Nature. "The molecules contain a ring structure and a chain of hydrocarbons, and are unique among known fluorescent molecules in animals."

These frogs, Hypsiboas punctatus, emit a significant amount of light. The scientists say the fluorescence "contributes 18-29% of the total emerging light under twilight and nocturnal scenarios, largely enhancing brightness of the individuals and matching the sensitivity of night vision in amphibians."

Or as the Nature article puts it, "about 18% as much visible light as a full Moon."

The frogs might use the fluorescence for communication, Lopes says, particularly to attract a mate.

In addition to sound and smell, this would allow a male to clearly signal his location to a female frog. "It's to coordinate the attraction," he says, "because it's specific for the frog eyes."

And while further study is required on the visual perception of this species of tree frog, Lopes says he suspects the light emitted is particularly exciting to the frog's eyes. Before this discovery, fluorescence was considered "irrelevant" to frog visual perception on land, according to the paper.

Lopes says there are other frogs with similar body structures and transparent skin, and that this discovery suggests fluorescence is likely more common than scientists previously thought. They're now researching other possible candidates, he says.

Julián Faivovich, a herpetologist at the University of Buenos Aires, tells Nature he wants other researchers to pitch in: "I'm really hoping that other colleagues will be very interested in this phenomenon, and they will start carrying a UV flashlight to the field."